Directional Architecture in Tensegrity Systems: Towards ‘Bone & Muscle’ Metamaterials

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The field of mechanical metamaterials has over the last decade seen dramatic progress, with the overarching goal to create a new generation of multifunctional and adaptive high-performance materials. Having demonstrated outstanding individual properties (e.g. ultra-strong nanolattices, shape-morphing origami structures), those characteristics are however largely incompatible due to fundamentally different design principles. To this day, there is no holistic concept how to synergetically implement true multifunctionality in mechanical metamaterials. Biological load-bearing structures, like bone-and-muscle physiologies, are based on so-called tensile-integrity, or tensegrity architectures and uniquely combine efficient material utilization with the ability to accommodate a broad variety of multifunctional tasks. In contrast to established metamaterial architectures, tensegrities are comprised of discontinuous compression members that are isolated from each other and only connected through a continuous network of tension members. Despite their mechanically unique topology, tensegrities have yet to be explored as metamaterial designs paradigm; the Emmy-Noether-Group aims to change thisInspired by biological bone-and-muscle physiologies, this Emmy-Noether-Group coalesces tensegrity principles and directional material, structure, and function designs into an architecture concept for a novel class of multifunctional tensegrity metamaterials. Across disciplines and scales, striking physical characteristics rely on highly directional effects and low-dimensional structures - from the unrivaled compressive stability of honeycombs to the extreme conductivity of carbon nanotubes. The presented concept provides an interdisciplinarily applicable approach that utilizes tensegrity principles to make these effects accessible in a volumetric metamaterial. In particular, the work program of this proposal focuses on the development of nano- and micro-tensegrities which are 3D-printed from polymer and pyrolyzed into ceramics. Thereby, tensegrity load-transfer mechanisms shall exploit pyrolysis contraction effects to induce directional material microstructure tailorability via controlled ultra-high tether straining. This is anticipated to provide a pathway to exploit extreme orientation- and size-dependent material properties, including CNT-like strength and stiffness. Simultaneously, control of tether straining and elastic bar buckling mechanisms are anticipated to program a wide range of stable reversible deformability with the intrinsically brittle constituent material. Based on that, the architecture concept will in subsequent efforts be expanded to the structure and function scale, where fiber actuation principles may be adopted to design tethers as artificial muscles and compressive bars could be modeled after natural cellular hierarchies like animal bones.